Decorative laminates have been conventionally made by stacking a plurality of layers of paper impregnated with thermosetting resins. Normally, the assembly consists of a plurality (for example, three to eight) of core sheets made from phenolic resin impregnated kraft paper, above which lies a decor sheet impregnated with melamine resin. An overlay sheet is provided on top of the decor sheet which, in the laminate, is essentially transparent and provides protection for the decor sheet.
Improvements of this process are disclosed in Scher et. al. U.S. Pat. Nos. 4,255,480; 4,263,081; 4,327,141; 4,395,452; 4,400,423; U.S. Re. No. 32,152; Ungar et. al. U.S. Pat. Nos. 4,713,138; and O'Dell et al. 4,567,087. These patents are commonly assigned herewith and their disclosures are incorporated by reference herein.
Scher et. al. U.S. Re. No. 32,152 teaches that compositions containing small mineral particles, which when coated without resin over unimpregnated printed paper, provide surprising and unexpected properties permitting such paper to be used in the preparation of decorative laminates without an overlay sheet. The resultant laminates are highly abrasion resistant.
This Scher coating composition is composed of a mixture of small particles of alumina or other abrasion resistant particles of average 20-50 micron particle size, and a lesser amount of micro-crystalline cellulose particles, both dispersed in a stable, aqueous slurry. The particles of alumina, of small size such that they do not interfere with the visual effects in the final product, serve as the abrasion resistant material and the micro-crystalline cellulose particles serve as the preferred temporary binder. Scher further teaches that the binder must be compatible with the resin system late utilized in the laminating procedure, usually melamine resin or in the case of certain low-pressure laminates a polyester resin system, and the micro-crystalline cellulose serves this function as well as stabilizing the small particles of alumina of the surface of the print sheet.
Ungar et. al. U.S. Pat. No. 4,713,138 teaches the process of depositing onto the surface of a decor sheet an ultra-thin layer of abrasion resistant material, which material is substantially disclosed in U.S. Pat. No. 4,255,480, simultaneously with the complete resin saturation of the decor sheet in a single step operation. The resin composition of the Ungar process acts as the carrier for the abrasion resistant material. The abrasion resistant composition consists essentially of an abrasion resistant hard mineral of fine particle size, preferably about 20-50 microns, in quantities sufficient to provide an abrasion resistant layer without interfering with visibility. The abrasion resistant mineral in Ungar is preferably alumina, silica or a mixture thereof. Ungar further teaches the use of a binder material for such mineral. The binder material in Ungar is present in an amount sufficient to bind the abrasion resistant mineral to the surface of the decor sheet. Such binder material is preferably a mixture of micro-crystalline cellulose with a minor amount carboxy methyl cellulose.
One such binder sold by FMC Corporation under the trademark "AVICEL" is a mixture of approximately 89% micro-crystalline cellulose and 11% carboxy methyl cellulose. The abrasion resistant composition suitably contains 1-8 parts by weight of "Avicel" to 4-32 parts by weight of mineral particles preferably at a ratio of mineral particles to binder material of 4:1 to 1:2, and a quantity of 1 part of "AVICEL" per 2 parts of mineral particles has been found to be particularly suitable.
Ungar et. al. also teaches that small additional quantities of carboxy methyl cellulose and a small quantity of silane may be added to the composition. Also, it is preferable to include a small quantity of surfactant, as disclosed in U.S. Pat. No. 4,255,480, and a small quantity of solid lubricant to provide scuff resistance, as disclosed in U.S. Pat. No. 4,567,087 in those compositions.
Accordingly, the above discussed patents provide single and two stage processes for providing a thin or ultra thin abrasion resistant laminate surface applied to decor sheets. However, it has been a continuing problem in the industry to provide a chemical, stain and abrasion resistant laminate surface on a decor sheet suitable for horizontal surfaces having certain brilliant visual appearance such as a pearlescent effect.
While considerable activity in the field has led to many decorative surface appearances, these activities resulted in the development of processes and compositions wherein the resin material was impregnated into the structure of the paper and the thin or ultra-thin layers of the laminate resin on the surface. The prior processes have failed to achieve laminate which meet all the international standards for horizontal laminate surfaces while retaining brilliant visual effects.